1. Field of the Invention
This invention relates to a mask structure for use in the lithographic processing technique and a process for preparing the same.
2. Description of the Prior Art
It has been widely utilized in the industry, particularly in the electronic industry, to produce various products by partially modifying the surfaces of workpieces according to a lithographic processing technique, which can mass-produce products having equally patterned, modified surface parts. Modification of workpiece surfaces is carried out by exposure to various energy beams, where an energy beam-shielding material is partially provided as a mask for forming a pattern. In the case that the energy beam to be irradiated is a visible light, glass, or a transparent substrate such as quartz, partially coated with a black light-shielding paint or partially provided with a visible light-nontransmissible thin sheet or film of such a metal as Ni or Cr, is used as a mask.
However, a fiber pattern formation and a lithographic processing technique for a shorter time have been recently in a keen demand, and thus X-ray, or particle beams such as ion beams, have been now utilized as an energy beam for irradiation. These energy beams are mostly absorbed by the glass plate or quartz plate used as a mask constituent member during the passage therethrough, as compared with the visible light. Thus, it is not preferable to use a glass plate or a quartz plate as a mask constituent member when these energy beams are used.
In the lithographic processing technique using X-ray or particle beams as an energy beam, various inorganic films, such as films of silicon nitride, boron nitride, silicon oxide, titanium, etc., or various organic films such as films of polyimide, polyamide, polyester, etc. or laminated films thereof are used as an energy-transmissible member, and a metal film such as films of gold, platinum, nickel, palladium, rhodium, or indium, is partially provided on the surface of said energy-transmissible member as an energy-absorbing member to prepare a mask. The mask itself is not self-supportable and thus must be supported on an appropriate support.
A lithographic mask structure has been so far prepared by forming a film comprising an X-ray-transmissible layer and a patterned X-ray-absorbing layer on a silicon wafer, and then removing the masked parts from the silicon wafer by etching. However, this process has many problems to be solved, particularly, in respect of the steps, time, and yield, for preparing the mask, which are the cause for delaying practical application of X-ray lithography.
FIG. 1 is a cross-sectional view of a conventional lithographic mask structure, and FIG. 2 is a plan view of its supporting substrate. Energy beam-absorbable mask members 3 are provided in a desired pattern on one side of energy beam-transmissible support film 2, and the peripheral part of the support film 2 is bonded to an annular support substrate 9 by an adhesive 8. No adhesive 8 is applied to the uppermost flat end surface 9a of annular support substrate 9 to improve the flatness, and the adhesive 8 is applied to the surface 9b which intersects at an angle .theta. with the flat end surface 9a at its outer peripheral side.
In the conventional mask structure as described above, the adhesive 8 extends not only between the support film 2 and the surface 9b, but also often over to the uppermost flat end surface 9a between the support film 2 and the annular support substrate 9. When the support substrate 9 is bonded to the support film 2. As a result, the flatness of support film 2 is often lowered. The lowering of the flatness leads to poor precision in the lithographic process.